I am not aware of any official rules, it comes down to engineering judgement and common sense.

I would start by considering the locked rotor current of the largest motor and the normal running of all other motors. Be generous, remembering that a 150 kva generator does not cost 50% more than a 100 kva machine.

An undersized generator could result in loss of life in an emergency, an oversized one costs only a little more and hurts nobody.

As far as the sprinkler pumps go, BS EN 12845 applies, and LPC TB210 may also apply. For domestic and residential BS 9251 applies. The requirement to size the generator based on 1 sprinkler pump stalled and the other starting comes from LPC TB210. There are a whole host of other requirements, too much to go into here but the basics are, for a BS EN 12845 / TB210 compliant installation, assuming 2 or more electric pumps:

• Electrical supply taken from the input side of the main switch if permitted. Confirmation of permission should be sought from the DNO / designer as appropriate.
• Supply to be available at all times.
• Dual sources of supply.
• Separate dual supplies to each pump.
• Fire-resistant diverse cable routes.
• HRC fuses.
• Automatic transfer switch (ATS) per pump.
• Pumps enclosed in 2 hour fire-resistant enclosure.
• Cable installation to BS 8519 (eg: enclosure of cables in areas of special fire risk, derating of cables in enclosures, cable selection meeting Category 3, separation of wiring from circuits provided for any other purpose and so on.)
• Supplies to be able to support LRA of one pump and start current of remaining pumps.

Good Morning

Your starting point would be BS 7671 Chapter 56 then BS 9991, BS 9999, BS 8519. The Fire Strategy for the building etc.

The generator must be able to pick up the load presented to it without stalling. You will need to get the data sheet for your chosen generator to verify what load it can pick up with a "crash transfer" normally something around 60% of the maximum output of the generator.

Fire pumps for hydrant mains are a big problem as fire engineers do not like variable speed drives as they contain electronics and they will want star delta starters for reliability. They come in pairs controlled by a panel which does the changeover and starting. If one has a locked rotor condition, bearing failure or the pump trying to digest a chunk of ice or half a house brick the fusing the pump fuses will operate before the supply fuses. If necessary the pumps have to be able to run to destruction. 

The fuel supply capacity has to meet the requirements for the Fire Strategy.

The Fire Engineer and the mechanical engineers have to do their design before you can put finger to keyboard.

JP

How 'huge' is the current involved for the locked sprinkler calc ? That one sounds quite sensible. - maybe in a fire  other loads are dropped (cookers water heaters etc may not be needed. )
Realise  that most gensets, unless specially designed with larger flywheels (which slows start up time) will stall if there is a load step of more than perhaps 1/3 to 1/2 of the full load. (unlike the normal mains that just dips a bit more than the 10% but keeps supplying current, unless the ADS trips )

Or how big is the mains supply you are trying to emulate?

Mike.

BSEN 12845 (Commercial) sprinklers and wet riser fire mains pumps don't have starters, just DOL contactors and then, as you say,  run to destruction. A generator may have support the full locked rotor current of one pump motor and then start the other DOL. Also support the full building load unless there is any form of load shedding.

The sprinkler supplier will have to tell you the locker rotor current and the maximum starting currents (effectively the same value) of the motors. It has to do this until the stalled motor burns out, so they will also have to tell you the burn out times for the motors, if they haven't already done so (they usually do).

Typically for a 10 storey building the current will be 800-1200A, so you would need a 1000kVA generator. For this reason it is usually more practicable to have a diesel motor on the secondary pump. The pump engine only has a single load to start and is far smaller than the generator would be.

regards, burn

I have 270A locked rotor plus 71A to start the other pump

Then add to that various smoke vent control panels, fire fighting lifts, lift sump pump....another good 100A

I just struggle to believe there is a scenario where all the above life safety services will be working at the same time and one sprinkler pump will lock rotor and start the second.

I think more along the lines of diversity however I dont know if I am allowed to apply any diversity

Thats why I am looking to see if there is any BS Standard that mentions generator sizing for life safety systems

Cheers

I can't remember which standard says it, but no, you can't allow diversity as such for life safety systems. You have to refer to the Fire Strategy, or ask the Fire Engineer. They risk assess it and usually only allow for a single fire in a building at any one time, meaning not all the systems will be needed simultaneously. This allows you to design for just the most onerous case.

There may be a BS for guidance but generators of a given size can have differing starting capabilities so you have to ask your specific manufacturer.

burn

well a 500kVA  machine is not so big .....

Mike.

... and don't forget to provide your generator manufacturer with loads expressed in kW as well as kVA. Often forgotten.

Star delta starting for electric sprinkler pumps